The present invention is an apparatus for use in serial radiography which provides replicable projection geometry between an energy source, an intraoral target area, and an image receptor.
The use of the radiograph as a tool for observation and diagnosis has played a significant role in the development of dental medicine. A single radiograph can reveal a multitude of information which is not available to the naked eye. One particularly useful application of the radiograph is serial radiography, in which two radiographs of a target area are compared to reveal changes occurring in that area during the time elapsed between exposures. Serial radiography is employed, for example, to recognize the loss of alveolar bone tissue which can result from periodontal disease. The technique is enhanced by digital subtraction, which uses computer analysis of digitized radiographs to locate areas of change between successive images.
To properly perform serial radiography, it is essential that the projection geometry of successive images be as near to identical as possible, since the discrepancies between two images with dissimilar projection geometry may mask areas in which tissue has been lost, or, conversely, may indicate loss of tissue where none has actually occurred. Within the prior art, one method has been developed to correct imaging errors resulting from misalignment of the x-ray source and image receptor between images which have no misalignment of the x-ray source and target area. However, no method has yet been developed to correct imaging errors resulting from misalignment of the x-ray source and the target area. As a result, the effectiveness of serial radiography for diagnosis of tissue loss is wholly dependent upon the ability of the radiographer to provide precise replication of projection geometry for every exposure.
In dental radiography, several types of devices for achieving satisfactory alignment of energy source, target area, and image receptor have been employed. One is the cephalostat, a device which by means of ear rods fixes a patient's head in a desired position bearing a fixed or otherwise known spatial relationship to an x-ray source. Stent based devices, in contrast, use a biting surface which is held between the teeth, and which provides alignment through some means extending from the biting surface toward the x-ray source. However, most devices of this type were developed before the advent of serial radiography, and therefore were not designed to provide alignment within the requisite tolerances. Several of these merit individual description.
Updegrave, U.S. Pat. No. 3,745,344, INTRAORAL SYSTEM FOR SUBSTANTIALLY CONFINING THE X-RAY BEAM TO THE FILM, Jul. 10, 1973, teaches a rectangular collimating tube which is affixed to and extends from an x-ray source toward a target area. A guide rod extending from the end of the collimating tube terminates in a bite plate which supports a film holder and which is held between the patient's teeth.
Maldonado, U.S. Pat. No. 4,554,676, DENTAL AIMING DEVICE, Nov. 19, 1985, teaches an aiming device comprising an alignment arm which terminates at one end in a bite plate supporting a film holder. The other end of the arm is fitted with an alignment ring to be positioned against the collimating tube of an x-ray source, thereby roughly achieving alignment between source, target, and film.
Angotti, U.S. Pat. No. 5,090,047, APPARATUS FOR POSITIONING AN IMAGE RECEPTOR FOR INTRAORAL DIAGNOSTICS, Feb. 18, 1992, teaches an aligning arm which is fixed at one end to the collimating tube of an x-ray source, and which terminates at the other end in a bite block and a film holder.
The prior art devices to date do not provide the optimal means for achieving replicable projection geometry. Devices such as Updegrave, which require visual alignment of two unconnected objects, do not restrict the patient's movement to within a range likely to reproduce a prior alignment, and do not supply a reliable reference surface for alignment. Conversely, devices such as Maldonado and Angotti rely solely on the mechanical integrity of a fixed system. A deformation or other alteration of the fixed alignment of the system with respect to the x-ray source, whether resulting from the movement of a patient or any other incident force, may render useless for purposes of comparison those radiographs taken before the alteration occurred. Additionally, the fixed nature of such devices may make them awkward for the patient to use.